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   源码介绍

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using System;
using System.Collections;
using System.Collections.Generic;
using System.Text;
using System.Net;
using System.Net.Sockets;
using System.Threading;
using System.Xml;
using System.IO;

namespace App.Core
{
    /// <summary>
    /// DNS服务器
    /// 运行程序,把网络协议中的DNS改为127.0.0.1,如果ping www.csdn.net,如果给出的地址是127.0.0.1,说明有效果 
    /// 目前只处理 A 类型的请求,其他一律转发给公共DNS服务器.
    /// </summary>
    public class DnsServer
    {
        protected System.Threading.Thread ListenThread = null;
        private Socket ServerSocket;
        public Hashtable IntranetMaps = new Hashtable();
        public Hashtable ExtranetMaps = new Hashtable();
        public IPEndPoint Forwarder;

        public DnsServer()
        {

        }

        public void LoadConfig()
        {
            try
            {
                if (!File.Exists(Fun.GetAppPath()   "\\Config.xml"))
                {
                    CreateConfigFile();
                }

                Xml xml = new Xml(Fun.GetAppPath()   "\\Config.xml");
                string debug = xml.GetText("//config/debug").ToLower();

                if (debug == "true" || debug == "1")
                {
                    Fun.DebugFlag = true;
                }

                // Forwarder当自己不知道的域名时转交给Forwarder处理
                string forwarderIP = xml.GetText("//config/forwarder").Trim();
                if (forwarderIP == "")
                {
                    forwarderIP = "60.191.244.5";
                }

                this.Forwarder = new IPEndPoint(IPAddress.Parse(forwarderIP), 53);//公共DNS服务器IP

                // 内网
                this.IntranetMaps.Clear();
                XmlNodeList xmlIntranetMaps = xml.GetNodes("//intranet/map");
                foreach (XmlNode xmlIntranetMap in xmlIntranetMaps)
                {
                    string domain = xml.GetAttribute(xmlIntranetMap, "domain".Trim());
                    string ip = xml.GetAttribute(xmlIntranetMap, "ip").Trim();

                    IntranetMaps[domain] = ip;
                }

                // 外网
                this.ExtranetMaps.Clear();
                XmlNodeList xmlExtranetMaps = xml.GetNodes("//extranet/map");
                foreach (XmlNode xmlExtranetMap in xmlExtranetMaps)
                {
                    string domain = xml.GetAttribute(xmlExtranetMap, "domain").Trim();
                    string ip = xml.GetAttribute(xmlExtranetMap, "ip").Trim();

                    ExtranetMaps[domain] = ip;
                }

            }
            catch (Exception ex)
            {
                Fun.Log(ex.Message);
            }
        }


        /// <summary>
        /// 当用udp.Send给某个不存在的节点(对方开端口)发送过数据，再调用udp.Receive就会跳出SocketException:远程主机强迫关闭了一个现有的连接
        /// 这是Socket的一个Bug
        /// </summary>
        public void FixUdpConnectionResetBug(Socket socket)
        {
            uint IOC_IN = 0x80000000;
            uint IOC_VENDOR = 0x18000000;
            uint SIO_UDP_CONNRESET = IOC_IN | IOC_VENDOR | 12;

            socket.IOControl((int)SIO_UDP_CONNRESET, new byte[] { Convert.ToByte(false) }, null);
        }

        public void RunThread()
        {
            // 线程
            this.ListenThread = new System.Threading.Thread(new ThreadStart(this.ListenThreadFunction));
            this.ListenThread.Start();

        }


        public void ListenThreadFunction()
        {
            LoadConfig();

            try
            {
                this.ServerSocket = new Socket(AddressFamily.InterNetwork, SocketType.Dgram, ProtocolType.Udp);
                FixUdpConnectionResetBug(this.ServerSocket);
                this.ServerSocket.Bind(new IPEndPoint(IPAddress.Any, 53));

                Fun.LogDebug("DnsServer Start");
            }
            catch (Exception ex)
            {
                Fun.Log(ex.Message);
                return;
            }

            while (true)
            {
                try
                {
                    DnsServerThread clientThread = new DnsServerThread(this);

                    EndPoint client = (EndPoint)new IPEndPoint(IPAddress.Any, 0);

                    clientThread.BufferLength = this.ServerSocket.ReceiveFrom(clientThread.Buffer, ref client);
                    clientThread.Client = (IPEndPoint)client;
                    clientThread.RunThread();
                }
                catch (Exception ex)
                {
                    Fun.Log("DnsServer Error:"   ex.Message);
                }
            }
        }

        // 因为多线程都要发，所以要同步
        public void SendToClient(byte[] bytes, EndPoint client)
        {
            lock (typeof(DnsServer))
            {
                this.ServerSocket.SendTo(bytes, client);
            }
        }


        // 自动创建配置文件
        public static void CreateConfigFile()
        {
            if (File.Exists(Fun.GetAppPath()   "\\Config.xml"))
            {
                return;
            }

            StringBuilder sb = new StringBuilder();
            sb.Append("<?xml version=\"1.0\" encoding=\"utf-8\"?>\r\n");
            sb.Append("<config>\r\n");
            sb.Append("  <debug>false</debug>\r\n");
            sb.Append("  <forwarder>60.191.244.5</forwarder>\r\n");
            sb.Append("  <heartbeaturl>http://heartbeat.ywu.cn/HeartBeat.aspx?System=Dns</heartbeaturl>\r\n");
            sb.Append("  <intranet>\r\n");
            sb.Append("      <map domain=\"www.goodluck.com\" ip=\"172.16.1.1\"/>\r\n");
            sb.Append("  </intranet>\r\n");
            sb.Append("  <extranet>\r\n");
            sb.Append("      <map domain=\"www.goodluck.com\" ip=\"60.191.227.188\"/>\r\n");
            sb.Append("  </extranet>\r\n");
            sb.Append("</config>\r\n");

            File.WriteAllText(Fun.GetAppPath()   "\\Config.xml", sb.ToString());
        }
    }
}